Control for heat pump and water heater



Get. 5, 1954 w. F. BORGERD CONTROL FOR HEAT PUMP AND WATER HEATER 2 Sheets-Sheet 1 Filed Oct. 15, 1951 Oct. 5, 1954 w. F. BORGERD CONTROL FOR HEAT PUMP AND WATER HEATER 2 Sheets-Sheet 2 Filed Oct. 15, 1951 N VHN Patented Oct. 5, 1954 was CONTROL FOR HEAT PUMP AND WATER HEATER William F. Borgerd, Evansville, Ind., assignor to International Harvester Company, a corporation of New Jersey Application October 15, 1951, Serial No. 251,381

19 Claims.

This invention relates generally to a control for a refrigeration system and more particularly to an automatic control system for a combination heat pump and water heater.

In my copending application titled Combination Heat Pump and Water Heater, filed October 15, 1951, Serial No. 251,380, there is described and claimed a combination heat pump and water heater. The combination disclosed therein comprises two heat exchange units connected in series to a motor-compressor assembly with means for reversing the flow of refrigerant through the units, and a water tank having a refrigerant coil which is connected to the compressors outlet and positioned in heat exchange relation with the water in the tank. The water will be quickly heated by the hot refrigerant gases during operation of the compressor, and by providing fan means for passing air from the enclosure into contact with one of the heat exchange units, the enclosure will be conditioned to a proper temperature range. The general purpose of the present invention is to provide automatic means for controlling the operation of the motor-compressor assembly and fan means.

Another object of the present invention is to provide automatic means for controlling the operation of the fan means and motor-compressor assembly in response to the temperature of the air within the enclosure.

Another object of the invention is to provide means for controlling operation of the motorcompressor assembly in response to the temperature of the water within the water tank.

Another object of the invention is to provide an electric circuit for the motor-compressor unit and fan means having means for breaking the circuit when overload conditions are encountered in order to prevent damage to the motor-compressor assembly.

Another object of the invention is to provide means for delaying the energization of the fan means for a predetermined period of time after the motor-compressor has been initially energized.

Another object of the invention is to provide the circuit with thermostatic means for automatically controlling the operation of the heat pump in response to the temperature of the air within the room during both the heating and cooling cycle.

Another object of the invention is to provide a thermal overload protector which will open the circuit when the temperature of the motor-compressor unit exceeds a safe maximum value.

Another object of the invention is to provide means for operating the motor-compressor unit while the fan means is inoperative in order that the high side temperature and pressure will be raised above normal values whereby the water 2 within said water tank will be heated to a higher temperature.

Another object is to provide the circuit with a high pressure cutout which automatically opens the circuit when the high side pressure of the refrigeration system exceeds a predetermined maximum value.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of the present invention is clearly shown.

In the drawings:

Fig. 1 is a diagrammatic view of the refrigeration system.

Fig. 2 is a simplified diagram of the control system for the refrigeration system.

Referring to Fig. 1 of the drawings, a combination heat pump and water heater system is diagrammatically represented. For a detailed description of this system reference may be had to the above mentioned copending application. The system comprises generally a motor-compressor unit It, a reversing valve l i, a room heat exchange unit l2, a basement heat exchange unit l3, and a submerged coil I4. The reversing Valve H is provided with a valve stem l5 which is slidably secured within the valve casing 1'5. The upper end of the valve stem 15 is connected to a lever I! which may be rotated to impart longitudinal movement to the valve stem. Four valve heads l8, I9, 20 and 2| are secured to valve stem IS in spaced relationship so that the valve heads i9 and 2| will seat when the valve stem is moved in one direction, and valve heads [8 and 20 will seat when the valve stem is moved in the opposite direction.

The motor-compressor unit It comprises an electric motor and a compressor hermetically sealed within an outer casing. -Electrical terminals 22 and 23 are provided for the electric motor and a refrigerant inlet 24 and outlet 25 are provided for the compressor.

It is contemplated that the finned tube room coil [2 either be located in an enclosure or room which is to be conditioned, or be connected to the rooms of a building by suitable ducts. An electric motor 26 is provided with a fan 21 which will circulate room air into heat exchange relation with the surface of the coil l2. The basement coil i3 can be positioned within the basement of the building or be connected thereto by ducts with fan means (not shown) for circulating the air from the basement into contact with the coil. The submerged coil I4 is enclosed by a casing 28 and is surrounded by a heat exchange liquid 29. The casing is provided with an inlet 30 and outlet 3| to which a coil 32 is connected with a pump 33 for circulating the liquid 29 therethrough. It is contemplated that coil 32 be buried in the ground so that the temperature of the earth surrounding the ground coil will remain constant throughout the year.

Reference numeral 34 designates a water tank in which a refrigerant coil 35 is disposed. The lower portion of the tank 34 is provided with a water inlet 36 which may be connected to a suitable water supply (not shown). A water out let 31 is connected into the upper portion of the tank 34 and it is contemplated that the water outlet be connected to the hot water faucets of the building in the usual manner whereby hot water from the tank can be supplied to various parts of the building.

Motor-compressor outlet is connected to coupling 38 which has one leg joined to conduit 39 and the other leg joined to conduit 40. The inlet oftank coil is joined to one end of conduit 40- and the outlet is connected to a reduced portion 4| of conduit 39 by conduit 42.

With lever in the horizontal position as shown in Fig. 1, valve heads l9 and 2| are in seated position and the heat pump will be operating to heat the building. Part of the com pressed refrigerant gases from the motor-compressor assembly l0 flows through conduit 39 and part flows through conduit 40 into coil 35 whereby the water within the tank 34 is heated. From the coil 35 the gases are returned to conduit 39 by conduit 42. The refrigerant gases then pass through valve conduit 43, receiver 44 and conduit 45 into room coil |2 where they will be condensed by the room air being circulated into contact with the coil by fan 21. The condensed refrigerant thenflows through conduit 46 into basement coil l3, where it will be further cooled by the basement air circulating thereover, then through conduit 41 and capillary restrictor tube 48. As the refrigerant passes through the restrictor tube 48, it changes from a high pressure to a low pressure and then flows through submerged coil I4 where it is vaporized by absorbing heat from the heat exchange liquid 29. These vapors then pass through conduit 49, valve H, and conduit 50- into the combination accumulator, strainer and drier 5| from which they are pulled into the motor-compressor unit I0 through conduit 52 to be recompressed and recirculated through the system. During the heating cycle, room coil I2 will be functioning as a condenser and basement coil 3 will be sub-cooling the liquid refrigerant so that the air being passed thereover will be heated to a desired temperature.

To change the system of the cooling cycle, lever I! is rotated so that valve stem I5 is moved upwardly to a position where valve heads l9 and 2| are unseated and valve heads l8 and 20 are seated. The compressed refrigerant vapors flow through coupling 38 and divide, part passing through conduit 39 and part passing through conduit 40 into tank coil 35. The water within the tank 34 is heated by coil 35 and the partially cooled refrigerant from the coil flows through conduit 42 into conduit 4|. The refrigerant vapors then pass through valve II and conduits 52 and 49 to the submerged coil l4 where the heat exchange liquid 29 cools and condenses the refrigerant within the coil. The liquefied refrigerant is forced through the capillary tube 48 into conduit 41 and through basement coil l3 and room coil I2 where it is vaporized by the heat absorbed by the air being circulated over the coils. The refrigerant vapors are returned to the motor-compressor unit It through conduit 45,

receiver 44, conduit 43, valve H. conduit 50, accumulator 5|, and conduit 52. Basement coil |'3 will cool and dehumidify the air within the basement and room coil l2 will maintain the room air within a predetermined temperature range.

Fig. 2 of the drawing shows an electric circuit and controls for the fan motor 26 and motorcompressor assembly I0. It comprises generally a cooling thermostatic switch 53, a heating thermostatic switch 54, a transformer 55, a solenoid switch 59, a time delay switch 57, a thermostatic switch |98, a pressure responsive switch 58, and. a control box 59. The control box comprises a non-conducting lever 90 having one end thereof pivotally connected at 6|. The opposite end of the. lever is connected by linkv 52 to a bellows 63 which is operated by a bulb 64 located in heat exchange relation with the water within tank 34. An intermediate portion of lever 60 is connected to an armature 65 of solenoid 66 which will pull the lever 60 upwardly when energized. Contact 61 is secured to lever 66 and is adapted to engage contact 68 when lever 69 is pulled upwardly by solenoid 66. Contact. 69 is secured to lever 60 and is arranged to engage fixed contact 10- when the lever 69 is pulled downwardly by bellows 63.

The primary coil 1| of the transformer 55 is connected by lines 72 and 13 to a suitable power source. To operate the heat pump, switch 14 is manually set to engage contacts ?5 and 76 when cooling is required or contacts I? and I8 when heating is required. Each of the thermostatic switches 53 and 54 comprises a fixed contact. 19 and a movable contact 80 which is secured to the movable end of a bi-metallic strip 3|. By way of example, when switch 74 is moved into engagement with contacts 75 and 16, bi-metallic strip 8| will move contact 89 into engagement with contact 19 when the room air requires cooling. It is contemplated that thermostats 53 and 54 be positioned within a room with switch 14 located in such a position that it can be easily reached by an operator. With contacts 19 and 89 in engagement, the circuit through secondary coil 82, line 83, thermostat 53, line 84, solenoid 66 and line will be com pleted. Solenoid 88 will also be energized through lines 86 and 81 which are connected to lines 84 and 85 respectively so that switch 56 is closed. Upon energization of solenoid 66, lever 69 will be pulled upwardly and contacts 61 and 68 will be brought into engagement.

Switch '56 will be closed simultaneously with the engagement of contacts 61 and 68 whereupon the circuit to the motor-compressor unit ID will be completed. This circuit comprises line 89, motor-compressor l9, switch I68, switch 58, line 95, switch 56, and line 9|. Fan motor 26 is connected in parallel with the motor-compressor unit H! by line 92, contacts 61 and 68, line 93, time delay switch 51, line 94, and line 95. As seen in Fig. 2, time delay switch 51 comprises a fixed contact 96 and a movable contact 91 which is fastened to bi-metallic strip 99. A resistor 99 is connected in parallel with contacts 96 and 91 by lines [BI and I92 so that current will flow therethrough. The bi-metallic strip 98 is calibrated so that after current has flowed through resistor 99 for approximately thirty seconds, the strip will be bent by the heat from the resistor and contact 9! will engage contact 96 whereby fan motor 26 is energized. By this arrangement the current surge from the fan motor 26 follows the heavy current surge from the motor-compressor It, and the temperature of coil I2 has been adjusted to normal before room air is blown thereover. Switch I08 is operated by a bellows I03 which is filled with a volatile fluid and positioned in close proximity to the motorcompressor unit II). The bellows I03 opens the switch I93 when the temperature of the unit exceeds a safe value. Switch 58 is operated by bellows i M which is connected to the compressor outlet 25 by tube I115. The bellows I04 automatically moves switch 58 to break the circuits to motor-compressor assembly ID when the high side pressure of the system raises beyond a predetermined maximum value.

After the room air has been cooled to a proper temperature, bi-metallic strip 3I will bend and move contact 80 away from contact I9 whereby the circuit to solenoid 83 and 63 will be broken. This causes switch 55 to be opened and contact 67 to be moved away from contact 68 whereby the circuit to motor-compressor assembly Ill and fan motor 26 is opened. When cooling is again needed, the circuits will be automatically closed by cooling thermostat 53. When the heat pump is to be operated to heat the building, lever II of reversing valve II is rotated to heating position and switch hi is moved into engagement with contacts ll and I8. Heating thermostat 54 will now automatically regulate the operation of motor-compressor assembly IS and fan motor 26 in response to room temperature.

In a heat pump system of the character illustrated, the high side temperature will probably range from 100 to 125 degrees Fahrenheit. For satisfactory home use, the water withdrawn from water tank 34 should be around 145 degrees Fahrenheit. Since the water will only be heated to approximately 120 degrees by the refrigerant coil during the regular cycling periods of the refrigeration system, it is contemplated that the motor-compressor Iii be operated for a, few minutes at the end of each runnin cycle. The operation of the motor-compressor is automatically controlled by bellows 63 of control box 59. This bellows is connected by tube I09 to the feeler bulb 54 which is filled with a volatile fluid and placed in heat exchange relation with the water within tank 34. The bellows 63 is set to pull lever 8E! downwardly as long as the Water temperature is below a predetermined value. The pull of solenoid 66 may be adjusted so that it will overcome the pull of bellows 63 whenever the circuit to the solenoid is closed. At the end of the running cycle, solenoid 66 will be deenergized and lever 50 will be pulled downwardly by bellows 63 to bring contacts 69 and Ill into engagement. This energizes the motor-compressor assembly is through line 89, switch I08, switch 58, line 535i, line I35, contacts It and 69, line I07, and line 6 I. The circuit to fan motor 26 remains open and no air will be circulated over room coil I2. The refrigerant will circulate through the system, but since fan 21 is not operating, only about one-third to one-half of the full capacity of the compressor will be used because of the limited size of the tank coil 35. This will cause the high side pressure and temperature to rise rapidly, and since a mixture of liquid and gas will be delivered to the capillary tube 48, this high pressure and temperature will be maintained. The increased temperature of the reirigerant flowing through tank coil 35 will heat the water to a corresponding higher temperature, and when the bulb 64 has been subjected to a predetermined temperature, bellows 6-3 will force lever 60 upwardly whereby contact 69 will be moved away from contact IE and the circuit to the motor-compressor It will be broken. In this way the water within tank 34 will be heated to approximately degrees Fahrenheit.

During a. few months out of the year, generally in the spring and fall, there are days when neither heating nor cooling of the room air is required. Since hot water is still required during such periods, it is contemplated that bellows 63 be used to control operation of'the motorcompressor assembly II]. By this arrangement the heat pump will operate to heat the water within tank 34, and since fan 21 is not operating, the air within the rooms of the building will not be affected.

As is apparent from the foregoing description, I have provided an effective control system for a combination heat pump and water heater. The operation of the refrigeration system is controlled by thermostatic means which are responsive to room air temperature. The energizing of the fan motor is delayed until after the motor-compressor assembly has started in order to reduce the total starting current and to allow the temperature of the room coil to be adjusted to a normal operating temperature before room air is circulated thereover. The control system provides means for running the motor-compressor assembly a short time after each cycling period in order that the water within the water tank will be heated to a high temperature by the increased high side temperature.

The invention is not to be understood as being limited to'the details described, since there may be modifications within the scope of the appended claims without departing from the spirit or scope of the invention.

Having thus described the invention, what I claim as new and desire to secure by Letters Patent is:

1. In a refrigeration system having a, motorcompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows there through, first means for operating said motorcompressor and said electric means in response to the temperature of said air, and second means for operating said motor-compressor independent of said electrical means in response to the temperature of the liquid.

2. In a refrigeration system having a motorcompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a first circuit connecting said motorcompressor to a power supply, a second circuit connecting said electric means to said power supply, means for opening and closing said circuits in respons to the temperature of said air, and means for opening and closing said first circuit independent of said second circuit in response to the temperature of said liquid.

3. In a refrigeration system haivng a motorcompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a first circuit connecting said motor-compressor to a power supply, a second circuit connecting said electric means to said power supply, means for opening and closing said circuits, and means for delaying energization of said electric means a predetermined time after said motor-compressor is energized.

4'. In a refrigeration system having a motorcompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a first circuit connecting said motor-compressor to a power supply, a second circuit connecting said electric means to said power supply, means for opening and closing said circuits in response to the temperature of said air, and means for breaking said circuits when the motor-compressor is overloaded.

5. In a refrigeration system having a motoroompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a first circuit connecting said motor-compressor to a power supply, a second circuit connecting said electric means to said power supply, means for opening and closing said circuits in response to the temperature of said air, means for delaying energization of said electric means a predetermined time after said motorcompressor is energized, and means for breaking said circuits when the motor-compressor is overloaded.

6. In a refrigeration system having a motorcompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a first circuit connecting said motor-compressor to a power supply, a second circuit connecting said electric means to said power supply, means for opening and closing said circuits in response to the temperature of said air, means for delaying energization of said electric means a predetermined time after said motorcompressor is energized, and means for breaking said circuits when the temperature of said motor-compressor reaches a predetermined value.

'7. In a refrigeration system having a motorcompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a first circuit connecting said motor-compressor to a power supply, a second circuit connecting said electric means to said power supply, means for opening and closing said circuits in response to the temperature of said air, means for delaying energization of said electric means a predetermined time after said motorcompressor is energized, and means for breaking said circuits when the high side pressure of said refrigeration system reaches a predetermined value.

8. In a refrigeration system having a motorcompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being comiected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a first circuit connecting said motor-compressor to a power supply, a second circuit connecting said electric means to said power supply, first means for opening and closing said circuits in response to the temperature of said air, second means for opening and closing said first circuit in response to the temperature of said liquid, and means for causing said second means to be inoperative when said first means has closed said circuits.

9. In a refrigeration system having a motorcompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a first circuit comiecting said m0- tor-compressor to a power supply, a second circuit connecting said electric means to said power supply, first means for opening and closing said circuits in response to the temperature of said air, second means for opening and closing said first circuit in response to the temperature of said liquid, means for causing said second means to be inoperative when said first means has closed said circuits, and means for delaying energization of said electric means a predetermined time after said motor-compressor is energized.

10. In a refrigeration system having a motorcompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a first circuit connecting said motor-compressor to a power supply, a second circuit connecting said electric means to said power supply, first means for opening and closing said circuits in response to the temperature of said air, second means for opening and closing said first circuit in response to the temperature of said liquid, means for causing said second means to be inoperative when said first means has closed said circuits, means for delaying energization of said electric means a predetermined time after said motor-compressor is energized, and means for breaking said circuits when the motor-compressor is overloaded.

11. In a refrigeration system having a motorcompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, means for operating said motor-compressor and said electric means when the air needs conditioning, and means for operating the motor compressor independent of said electric means when the liquid requires heating.

12. In a refrigeration system having a motorcompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a circuit connecting said motor-compressor and said electric means to a power supply, thermostatic means for opening and closing said circuit, a switch for delaying energization of said electric means a predetermined time after said motor-compressor is energized, a thermostatic switch for breaking the circuit when the temperature of said motor-compressor reaches a predetermined value, and a pressure operated switch for breaking the circuit when the high side pressure reaches a predetermined value.

13. In a refrigeration system having a motorcompressor and a heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a circuit connecting said motor-compressor to a power supply, thermostatic means for opening and closing said circuit in response to the temperature of said air, a thermostatic switch for opening and closing said circuit in response to the temperature of said liquid, and means for maintaining said thermostatic switch in open position when said thermostatic means is in closed position.

14. In a refrigeration system having a motorcompressor and a heat exchange unit, a coil positioned in heat exchange relation with a liquid,

said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a circuit connecting said motor-compressor to a power supply, thermostatic means for opening and closing said circuit in response to the temperature of said air, a thermostatic switch for opening and closing said circuit in response to the temperature of said liquid, and a solenoid which is energized when said circuit is closed, said solenoid acting to hold said thermostatic switch in open position when energized.

15. In a refrigeration system having a motorcompressor and a heat exchange .unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a first circuit connecting said motorcompressor to a power supply, a second circuit connecting said electric means to said power supply, thermostatic means for opening and closing said circuits in response to the temperature of said air, a thermostatic switch for opening and closing said first circuit in response to the temperature of said liquid, electromagnetic means for holding said thermostatic switch in open position when said thermostatic means has closed said circuits.

16. In a refrigeration system having a motorcompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a first circuit connecting said motorcompressor to a power supply, a second circuit connecting said electric means to said power supply, thermostatic means for opening and closing said circuits in response to the temperature of said air, a time delay switch for delaying energization of said electric means a predetermined period of time after the motor-compressor is energized, and a thermostatic switch for opening and closing said first circuit in response to the temperature of said liquid.

17. In a refrigeration system having a motorcompressor and a heat exchange unit, electric means for circulating air to be conditioned over said heat exchange unit, a coil positioned in heat exchange relation with a liquid, said coil being connected to said motor-compressor so that a portion of the compressed refrigerant flows therethrough, a first circuit connecting said motorcompressor to a power supply, a second circuit connecting said electric means to said power sup ply, thermostatic means for opening and closing said circuits in response to the temperature of said air, a time delay switch for delaying energization of said electric means a predetermined period of time after the motor-compressor is energized, a thermostatic switch for opening and closing said first circuit in response to the temperature of said liquid, and electro-magnetic means for holding said thermostatic switch in open position when said thermostatic means has closed said circuits.

18. In a refrigeration system, a motor-compressor unit, a heat exchange unit mounted to cooperate with air to be conditioned and connected to said motor-compressor unit, electric means operable to circulate said air over said heat exchange unit, a liquid, a coil mounted in a heat exchange relationship with said liquid, a refrigerant charging said system, said coil being connected to the outlet and inlet of said motorcompressor unit so that a portion of said refrigerant flowing from the outlet of said motorcompressor unit and into the inlet of said motorcompressor unit passes through said coil when said motor-compressor unit is operating, first means operating responsive to the temperature of said air for simultaneously operating said motor-compressor unit and said electric means, and second means operating responsive to the temperature of said liquid for operating said motor-compressor unit independent of said electric means.

19. In a refrigeration system, a motor-compressor unit, a heat exchange unit mounted to cooperate with air to be conditioned and connected to said motor-compressor unit, electric means operable to circulate said air over said heat exchange unit, a liquid, a coil mounted in a heat exchange relationship with said liquid, a refrigerant charging said system, said coil being connected to the outlet and inlet of said motorcompressor unit so that a portion of said refrigerant flowing from the outlet of said motorcompressor unit and into the inlet of said motorcompressor unit passes through said coil when said motor-compressor unit is operating, a thermostat operating responsive to the temperature of said air, a first circuit including said first thermostat, said motor-compressor unit and said electric means, for simultaneously operating said motor-compressor unit and said electric means responsive to the operation of said first thermostat, a second thermostat operating responsive to the temperature of said liquid, and a second circuit including said motor-compressor unit and said second thermostat for operating said motorcompressor unit independent of said electric means responsive to the operation of said second thermostat.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,874,803 Reed Aug. 30, 1932 2,135,285 Gibson Nov. 1, 1938 2,241,070 McLenegen May 6, 1941 2,492,970 Curry Jan. 3, 1950 2,575,325 Ambrose Nov. 20, 1951 

